The present invention relates to an optical element.
Articles that need to be protected against forgery, such as securities, certificates, and upscale brand name products, are known to have optical elements that prevent forgery of the articles. Such optical elements provide optical effects that are difficult to reproduce. Examples of such optical elements include holograms, diffraction gratings, and multilayer interference films. These optical elements have minute structures or complex layered structures, which hinder analysis of the structures of the optical elements. This prevents counterfeiting of the optical elements, thereby limiting forgery of the articles with such optical elements.
An optical element such as a hologram includes a reflection layer, which is in contact with a diffraction structure to enhance the optical effect of the element. In such a structure, the difficulty in reproducing the hologram can be increased by shaping the reflection layer in a predetermined pattern (see Japanese Laid-Open Patent Publication No. 2003-255115 for example).
In order to increase the difficulty in reproducing the optical effects of optical elements, it is desirable that a single optical element provide additional optical effects. Addition of optical effects to an optical element has been desired not only for an optical element that is used to prevent forgery of articles described above, but also for an optical element that is attached to an article for decoration and an optical element that is appreciated for its own aesthetic quality.